Petrology of Karoo volcanic rocks in the southern Lebombo monocline,Mozambique |
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| Institution: | 1. Department of Cardiology, Papworth Hospital, Cambridge, UK;2. Department of Cardiology, Royal Brompton Hospital, London and Biomedical Research Unit, Royal Brompton and Harefield NHS Trust and Imperial College London, UK;3. Department of Cardiology, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA;4. Department of Cardiac Physiology, Papworth Hospital, Cambridge, UK;1. Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin 300211, People''s Republic of China;2. Key Laboratory of Hormones and Development (Ministry of Health), Department of Diabetes and Gout, Metabolic Disease Hospital & Tianjin Institute of Endocrinology, Tianjin Medical University, Tianjin 300070, People''s Republic of China;1. Department of Cardiovascular Research, King''s College London, James Black Centre, 125 Coldharbour Lane, London SE5 9NU, United Kingdom;2. Kings College Hospital NHS Foundation Trust, Denmark Hill, London SE5 9RS, United Kingdom;1. Division of Cardiology, Department of Medical and Surgical Sciences, University Magna Graecia, Catanzaro, Italy;2. Division of Nuclear Medicine, Department of Experimental and Clinical Medicine, University Magna Graecia, Catanzaro, Italy;3. Laboratory of Clinical Biochemistry and Molecular Biology, Department of Experimental and Clinical Medicine, University Magna Graecia, Catanzaro, Italy;4. U.R.T.-C.N.R., Catanzaro, Italy |
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| Abstract: | The Karoo volcanic sequence in the southern Lebombo monocline in Mozambique contains different silicic units in the form of pyroclastic rocks, and two different basalt types. The silicic units in the lower part of the Lebombo sequence are formed by a lower unit of dacites and rhyolites (67–80 wt.% SiO2) with high Ba (990–2500 ppm), Zr (800–1100 ppm) and Y (130–240 ppm), which are part of the Jozini–Mbuluzi Formation, followed by a second unit, interlayered with the Movene basalts, of high-SiO2 rhyolites (76–78 wt.%; the Sica Beds Formation), with low Sr (19–54 ppm), Zr (340–480 ppm) and Ba (330–850 ppm) plus rare quartz-trachytes (64–66 wt.% SiO2), with high Nb and Rb contents (240–250 and 370–381 ppm, respectively), and relatively low Zr (450–460 ppm). The mafic rocks found at the top of the sequence are basalts and ferrobasalts belonging to the Movene Formation. The basalts have roughly flat mantle-normalized incompatible element patterns, with abundances of the most incompatible elements not higher than 25 times primitive mantle. The ferrobasalt has TiO2 ～ 4.7 wt.%, Fe2O3t = 16 wt.%, and high Y (100 ppm), Zr (420 ppm) and Ba (1000 ppm). The Movene basalts have initial (at 180 Ma) 87Sr/86Sr = 0.7052–0.7054 and 143Nd/144Nd = 0.51232, and the Movene ferrobasalt has even lower 87Sr/86Sr (0.70377) and higher 143Nd/144Nd (0.51259). The silicic rocks show a modest range of initial Sr-(87Sr/86Sr = 0.70470–0.70648) and Nd-(143Nd/144Nd = 0.51223–0.51243) isotope ratios. The less evolved dacites could have been formed after crystal fractionation of oxide-rich gabbroic cumulates from mafic parental magmas, whereas the most silica-rich rhyolites could have been formed after fractional crystallization of feldspars, pyroxenes, oxides, zircon and apatite from a parental dacite magma. The composition of the Movene basalts imply different feeding systems from those of the underlying Sabie River basalts. |
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